One of the primary factors in assessing specific mechanisms of brain aging is high quality animal care. One of the most common confounding variables in aging studies are inconsistent animal care, non-specific stress, and the presence of unrecognized age-related pathologies that compromise the dependent variables under investigation. For these reasons (and others), the Animal Core within the PPG must be of the highest quality. In the past funding period, this Core has been successful in maintaining animals in specific pathogen free (SPF) conditions for project studies, in developing and providing extensive validation of a novel model of adult-onset growth hormone deficiency that will continue to be used in the proposed funding period. This model provides a unique resource for the Program Project and opportunity to investigate the effects of growth hormone deficiency apart from other factors that may contribute to brain aging. The Animal Core has multiple aims: 1) The Core will procure and maintain animals used by program investigators and meet all AAALAC and institutional standards for animal care in the satellite facilities. The Core will also maintain a breeding colony of dw/+ (female) and dw/dw (male) Lewis rats and raise offspring to be used for the model of adult-onset growth hormone deficiency proposed in this application. The Core will coordinate animal/tissue use among the projects. 2) The Core personnel will assess basic parameters of aging animals and monitor sentinel and experimental animals for the presence of disease. 3) The Core will provide surgical services. 4) The Core will be responsible for irradiation of animals, as necessary, and measure hormone levels in tissue. 5) The Core will conduct behavioral analyses on animals to assess age-related alterations in hippocampally dependent measures of learning and memory and will develop frontal-lobe dependent tasks of learning and memory. The Animal Core is an essential aspect of the Program Project ensuring effective management of limited resources, smooth interactions between projects and the use of animal models that have been extensively validated for studies of the biology of aging.